Psoriasis - Causes

Highlights	Diagnosis	Managing Psoriasis
Introduction	Treatment	Outlook
Types of Psoriasis	Topical Medications	Resources
Causes	Systemic Medications	References
Risk Factors	Phototherapy

Types of Psoriasis

Various forms of psoriasis exist. Some can occur alone or at the same time as other types, or one may follow another. The most common type is called plaque psoriasis, also known as psoriasis vulgaris.

Plaque Psoriasis

Plaque psoriasis leads to skin patches that start off in small areas, about 1/8 of an inch wide. They usually appear in the same areas on opposite sides of the body.

The patches slowly grow larger and develop thick, dry plaque. If the plaque is scratched or scraped, bleeding spots the sizes of pinheads appear underneath. This is known as the Auspitz sign.

Some patches may become ring-shaped (annular), with a clear center and scaly raised borders that may appear wavy and snake-like.

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As the disease progresses, eventually separate patches may join together to form larger areas. In some cases, the patches can become very large and cover wide areas of the back or chest. These are known as geographic plaques because the skin lesions resemble maps.

Plaque psoriasis may persist for long periods of time. More often it flares up periodically, triggered by certain factors such as cold weather, infection, or stress.

Patches most often occur on the:

Elbows
Knees
Lower back

They may also be seen on the:

Upper pelvic bone area
Bottom of the feet
Calves and thighs
Genital areas
Palms of the hands

Psoriasis of the scalp affects about 50% of patients. In some cases, the psoriasis may cover the scalp with thick plaques that extend down from the hairline to the forehead.

Psoriasis patches rarely affect the face in adulthood. In children, psoriasis is most likely to start in the scalp and spread to other parts of the body. Unlike in adults, it also may occur on the face and ears.

Less Common Forms of Psoriasis
Psoriasis Form	Description of Skin Patches	Comments
Guttate Psoriasis	The patches are teardrop-shaped and appear suddenly, usually over the trunk and often on the arms, legs, or scalp. They often disappear without treatment.	Guttate psoriasis can occur as the initial outbreak of psoriasis, often in children and young adults 1 - 3 weeks after a viral or bacterial (usually streptococcal) respiratory or throat infection. A family history of psoriasis and stressful life events are also highly linked with the start of guttate psoriasis. Guttate psoriasis can also develop in patients who have already had other forms of psoriasis, most often in people treated with widely-applied topical (rub-on) products containing corticosteroids.
Inverse Psoriasis	Patches usually appear as smooth inflamed areas without a scaly surface. They occur in the folds of the skin, such as under the armpits or breast, or in the groin.	Inverse psoriasis may be especially difficult to treat.
Seborrheic Psoriasis	Patches appear as red scaly areas on the scalp, behind the ears, above the shoulder blades, in the armpits or groin, or in the center of the face.	Seborrheic psoriasis may be especially difficult to treat.
Nail Psoriasis	Tiny white pits are scattered in groups across the nail. Toenails and sometimes fingernails may have yellowish spots. Long ridges may also develop across and down the nail. The nail bed often separates from the skin of the finger and collections of dead skin can build up underneath the nail.	Over half of patients with psoriasis have abnormal changes in their nails, which may appear before other skin symptoms. In some cases, nail psoriasis is the only symptom. Nail psoriasis is linked to psoriatic arthritis.
Generalized Erythrodermic Psoriasis (also called psoriatic exfoliative erythroderma)	This is a rare and severe form of psoriasis, in which the skin surface becomes scaly and red. The disease covers all or nearly all of the body.	About 20% of such cases evolve from psoriasis itself. The condition may also be triggered by certain psoriasis treatments, and other medications such as corticosteroids or synthetic antimalarial drugs.
Pustular Psoriasis	Patches become pus-filled and blister-like. The blisters eventually turn brown and form a scaly crust or peel off. Pustules usually appear on the hands and feet. When they form on the palms and soles, the condition is called palmar-plantar pustulosis.	Pustular psoriasis may erupt as the first occurrence of psoriasis, or it may evolve from plaque psoriasis. A number of conditions may trigger pustular psoriasis, including infection, pregnancy, certain drugs, and metal allergies. Pustular psoriasis can also accompany other forms of psoriasis and can be very severe.